The subject matter disclosed herein relates to an aircraft and, more particularly, to a helicopter with a rotor, an auxiliary propeller and an automatic propeller torque protection system for engine failure rotor droop avoidance.
Some helicopters, such as a coaxial helicopter, may include one or more rotors to provide lift and one or more propellers to provide thrust. The main rotor(s) include a hub(s) and blades extending outwardly from the hub(s). The blades rotate about the center of the hub to provide lifting forces and control forces and moments to control the vehicle. The pitch (feathering angle) of each of the main rotor blades is controlled in order to manipulate the induced forces and moments. The propeller(s) also include a hub and blades that rotate to induce thrust to provide additional forces and moments to control the aircraft, which can be manipulated as control inputs.
The aircraft further includes one or more engines and one or more transmissions. The engine provides power to drive rotation of the main rotor(s) and the propeller(s). The transmission(s) transmit power from the engine(s) to the main rotor(s) and propeller(s).
While such a helicopter is flying at high speeds, a significant percentage of the aircraft engine power is required to drive the propeller in order to provide thrust. In the event of an engine failure, power can no longer be provided from the engine(s) to the main rotor(s) or the propeller(s). The objective of the aircraft pilot during this engine failure condition is to rapidly decrease the pitch of the propeller blades in order to remove the propeller torque demand and to use the vehicle potential and kinetic energy to keep the main rotor(s) spinning. The main rotor rotational energy conservation is critical to control the aircraft in a descent to a landing spot, arrest the descent rate once close to the ground, and land safely before the rotor stops turning and can no longer provide lift and control. The pilot response delay and fidelity in the event of engine failure tends to be insufficient to remove the propeller torque demand prior to main rotor rotational speed reduction. Further, the workload to decrease the propeller pitch precisely is high, and the pilot must watch the display to set the proper propeller pitch command, thus reducing their “eyes out the window” situational awareness and their attention to other control inputs.